arm64: efi: enable generic EFI compressed boot

Wire up the generic EFI zboot support for arm64.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Jeremy Linton <jeremy.linton@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/Makefile

@@ -151,12 +151,17 @@ libs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
 
 # Default target when executing plain make
 boot		:= arch/arm64/boot
+
+ifeq ($(CONFIG_EFI_ZBOOT),)
 KBUILD_IMAGE	:= $(boot)/Image.gz
+else
+KBUILD_IMAGE	:= $(boot)/vmlinuz.efi
+endif
 
-all:	Image.gz
+all:	$(notdir $(KBUILD_IMAGE))
 
 
-Image: vmlinux
+Image vmlinuz.efi: vmlinux
 	$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
 
 Image.%: Image

arch/arm64/boot/.gitignore

 # SPDX-License-Identifier: GPL-2.0-only
 Image
 Image.gz
+vmlinuz*

arch/arm64/boot/Makefile

@@ -38,3 +38,9 @@ $(obj)/Image.lzo: $(obj)/Image FORCE
 
 $(obj)/Image.zst: $(obj)/Image FORCE
 	$(call if_changed,zstd)
+
+EFI_ZBOOT_PAYLOAD	:= Image
+EFI_ZBOOT_BFD_TARGET	:= elf64-littleaarch64
+EFI_ZBOOT_MACH_TYPE	:= ARM64
+
+include $(srctree)/drivers/firmware/efi/libstub/Makefile.zboot